Sabot projectiles are used when an oversized gun tube launches a subcaliber warhead. These projectiles have sabot petals or segments wrapped around the warhead and contact the bore of the gun tube during ejection. The sabot seals the bore to prevent escape of the propulsion gases during firing and then drops away from the warhead when it leaves the gun tube. One such projectile is an armor piercing, fin stabilized discarding sabot which has three sabot sections around a central core or body. These sections are held together with a front bourrelet and a band or obturator at the rear. A fin assembly stabilizes the central core in flight.
During firing, a gas tight seal is necessary between the discarding sabot and the subprojectile body within it. Gas leakage in this area greatly increases the potential for unstable launches and for projectile parts breakup. The latter condition can also result in damage to the gun tube. Any means utilized for obtaining such a seal, however, must not interfere with the subsequent separation of the sabot segments or with the flight of the projectile after it has left the gun tube.
At present, base seals are molded over the rear end of the sabot/core assembly. Generally, this type of seal works well except when firing through a worn gun tube. As the gun tube wears, the internal bore becomes enlarged. This permits some radial expansion of the sabot segments during firing. Frequently, this expansion is sufficient to rupture the conventional molded seal before the projectile has left the gun tube. The ruptured seal and displaced sabot segments permit the propulsion gases to flow between the core and the sabot segments, thus creating the undesireable conditions previously stated.